Preliminary for dropping releae-fast profile

Author: oech3

src/uucore/src/lib/mods/error.rs

@@ -52,7 +52,7 @@
 //! * Using [`ExitCode`] is not recommended but can be useful for converting utils to use
 //!   [`UResult`].
 
-// spell-checker:ignore uioerror rustdoc
+// spell-checker:ignore codegen-units uioerror rustdoc
 
 use std::{
     cell::Cell,
@@ -394,13 +394,20 @@ impl UIoError {
     #[allow(clippy::new_ret_no_self)]
     /// Create a new `UIoError` with a given exit code and message.
     pub fn new<S: Into<String>>(kind: std::io::ErrorKind, context: S) -> Box<dyn UError> {
-        Box::new(Self {
-            context: Some(context.into()),
-            inner: kind.into(),
-        })
+        cold_io_error(kind, context.into())
     }
 }
 
+// avoid performance regression with codegen-units=1
+#[cold]
+#[inline(never)]
+fn cold_io_error(kind: std::io::ErrorKind, context: String) -> Box<dyn UError> {
+    Box::new(UIoError {
+        context: Some(context),
+        inner: kind.into(),
+    })
+}
+
 impl UError for UIoError {}
 
 impl Error for UIoError {}